Make sure the SCSI host properly defines the DLT1 tape drive by confirming that the drive is identified as a DLT1 and that the appropriate device driver is loaded. Only use drivers provided by Dell. These drivers can be downloaded from support.dell.com. If a SCSI host does not recognize the product identification string of the drive returned by an inquiry command, the host may disable the internal cache on that drive. If the internal cache is disabled, the DLT1 tape drive''s performance can be reduced to 100KB/second or less.

Record Size and Type

In general, fixed-length records, or blocks, maximize the throughput and the bigger the record the better. With data compression off, record sizes should be 32KB or even 64KB in size. Using 64-KB records should result in throughput in the 3MB/second range. Many backup applications default to a smaller record size, which will reduce the throughput performance of the drive.

Data Compression

Different types of data compress differently. Low compression ratios will produce slower performance. Graphics and video files, such as JPEG and MPEG files, as well as zipped files, are already compressed. In the Novell environment, entire volumes are often pre-compressed. Compressed files may actually expand slightly when the tape drive attempts to re-compress them. Other file types, such as executables, do not compress easily. For these reasons, it is not uncommon to experience less than a 2:1 compression ratio, achieving less than the specified compressed capacity of the data cartridge. This will affect the performance of the DLT1 drive because the drive will actually have to store more data.

Many backup applications provide the option of using either hardware or software data compression. When possible, use hardware compression; it is generally more efficient than software compression.

NOTE:It is never beneficial to enable both hardware and software compression at the same time.

Network Conditions

Often, when backing up network drives, the network bandwidth, traffic, and other factors limit performance. Compare the time it takes to complete a remote backup to that required for a local backup. If your local backup is faster, the performance decrease that you are experiencing is probably related to the network and not to your tape drive.

Number, Size, and Location of Files to be Backed Up

The size and number of files included in a backup affects performance. The fastest backups occur when the disk contains a few large files. Slower backups occur when the disk contains large numbers of small files. If the files are in the same directory path, performance will be higher; the more directories you have in which the files are being stored, the slower your performance will be when backing them up.

Host System Configuration

Host processor speed, host adapter performance, bus configuration, host software, and performance of the hard drive are also factors affecting backup performance. It is often possible to get a sense for the maximum data transfer rate possible, regardless of the DLT1 tape drive, by copying to a null file on disk. When this transfer rate is lower than the DLT1 tape drive throughput specifications, it is likely that improvements will have to be made in the host before the DLT1 drive can reach its maximum transfer rate.

What variables could interfere with the backup performance of my Dell™ PowerVault™ 110T or 120T DLT1 tape drive?

There are a number of variables that can affect the backup performance of your DLT1 tape drive. Among the most important are:

SCSI host adapter drivers

Record size and type

Data compression

Network conditions

Number, size, and location of files to be backed up

Host system configuration

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